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Nothing affects your HVAC system’s performance like its size. Decades ago, the Air Conditioner Contractors of America developed a way to standardize the sizing process, for both the HVAC unit and ductwork. These protocols, called Manual J and Manual D, respectively, provide a precise way to size a cooling or heating system for a home. Manual J goes far beyond just using the square footage of your home and such elements as:

  • Cubic footage
  • Insulation levels
  • Window efficiency and exposure to the sun
  • Heat-producing appliances and your lighting types
  • Rate of air infiltration
  • Outdoor landscaping
  • Number of occupants in the home and their ages
  • Preferred temperature settings
  • Lifestyle factors

The end result tells what tonnage of cooling or heating system is necessary for optimal performance in your home. Although it may seem that bigger is better, it’s not the case when it comes to your air conditioner. In fact, it’s better to choose a system that’s slightly too small than too large.

When an air conditioner is too big, it runs in short cycles. It won’t remove enough humidity inside to keep your air comfortable. It also turns on more frequently, which drives up your electric bill and adds wear and tear to the equipment. If your HVAC contractor comes to your home and doesn’t measure your windows, inspect your insulation or factor in the layout of your home when sizing the ductwork, you could end up with an improperly sized system.

Using Manual J also provides a road map for you to start improving the energy efficiency of your home. As the contractor goes through the sizing process, ask him where your home’s energy deficiencies are. You might be able to improve the factors that drive the cooling and heating loads inside your home, allowing you to select a smaller and cheaper system.

If you’d like to learn more about Manual J and its companion, Manual D, contact NisAir Air Conditioning and Heating. We’ve provided HVAC services for Martin, Palm Beach, St. Lucie and Indian River counties since 1973.

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